That is to say, the「orifice has opened when the foot-binding cloth has been removed」and here refers to a gawking mouth, likened to a SURPRISED person (perhaps…there are other interpretations, such as gasping at the moment of orgasm):「person with rod in arch of no-longer-integrated foot orifice.」Frankly, seeing inside that arch might cause anyone to GAWK IN SHOCK:.
Men in dynastic China masturbated by wrapping an erect penis with no-longer-integrated feet: see Chinese erotic art for details.「…Bound feet were once considered intensely erotic in Chinese culture…. Qing Dynasty sex manuals listed 48 different ways of playing with women's bound feet. …Women, their families, and [a husband] took great pride in tiny feet, with the ideal length, called the 'Golden Lotus,' being about 7 cm (2.75 inches) long.」
「…The process was started before the arch of the foot had a chance to develop fully, usually between the ages of 2 and 5. Binding usually started during the winter months since the feet were more likely to be numb, and therefore the pain would not be as extreme. …To enable the size of the feet to be reduced, the toes on each foot were curled under, then pressed with great force downwards and squeezed into the sole of the foot until the toes broke. The broken toes were held tightly against the sole of the foot while the foot was then drawn down straight with the leg and the arch forcibly broken. The bandages were repeatedly wound in a figure-eight movement, starting at the inside of the foot at the instep, then carried over the toes, under the foot, and around the heel, the freshly broken toes being pressed tightly into the sole of the foot. At each pass around the foot, the binding cloth was tightened, pulling the ball of the foot and the heel together, causing the broken foot to fold at the arch, and pressing the toes underneath. …It was generally an elder female member of the girl's family or a professional foot binder who carried out the initial breaking and ongoing binding of the feet. This was considered preferable to having the mother do it, as she might have been sympathetic to her daughter's pain and less willing to keep the bindings tight.」
「…The tightness of the binding meant that the circulation in the feet was faulty, and the circulation to the toes was almost cut off, so any injuries to the toes were unlikely to heal and were likely to gradually worsen and lead to infected toes and rotting flesh. If the infection in the feet and toes entered the bones, it could cause them to soften, which could result in toes dropping off. Although, this was seen as a benefit because the feet could then be bound even more tightly. Girls whose toes were more fleshy would sometimes have shards of glass or pieces of broken tiles inserted within the binding next to her feet and between her toes to cause injury and introduce infection deliberately. Disease inevitably followed infection, meaning that death from septic shock could result from foot-binding, and a surviving girl was more at risk for medical problems as she grew older.」
「At the beginning of the binding, many of the foot bones would remain broken, often for years. However, as the girl grew older, the bones would begin to heal. Even after the foot bones had healed, they were prone to re-breaking repeatedly, especially when the girl was in her teenage years and her feet were still soft.」
[ https://en.wikipedia.org/wiki/Foot_binding 2012-12-17, emphasis ours ]

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: expression of surprise
Japanese EDRDG: expression of surprise
Unihan extended: exclamation of surprise